Maleic anhydride grafted LLDPE having high melt index

ABSTRACT

Disclosed is a linear low-density polyethylene grafted with maleic anhydride (MAH-g-LLDPE). The MAH-g-LLDPE has a unique combination of properties including a low density and a high melt index.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date of ProvisionalApplication No. 62/038,078 filed Aug. 15, 2014; the entire content ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention generally relates to linear low-density polyethylenes(LLDPEs) grafted with maleic anhydride, their uses, and processes formaking them.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,194,509 discloses peroxide-free grafting of homopolymersand copolymers of ethylene having densities equal to or greater than0.930 g/cm³. While exhibiting improved adhesion, the grafted polymershave a low melt index (<4 g/10 min).

U.S. Pat. No. 6,433,133 B1 discloses a process for reducing the weightaverage molecular weight and melt index ratio of polyethylenes. Thepolyethylenes may be grafted. The grafted polyethylenes have a meltindex only as high as 37 g/10 min.

There is a need in the art for maleic anhydride grafted LLDPEs that haveimproved properties, such as greater adhesion over a wide temperaturewindow.

The present invention addresses this need as well as others, which willbecome apparent from the following description and the appended claims.

SUMMARY OF THE INVENTION

The invention is as set forth in the appended claims.

Briefly, in one aspect, the present invention provides a linearlow-density polyethylene (LLDPE) grafted with maleic anhydride(MAH-g-PE). The MAH-g-LLDPE has a melt index (MI) of 250 to 800 g/10minutes and comprises 0.01 to 3 weight percent of maleic anhydride,based on the weight of the MAH-g-LLDPE.

The MAH-g-LLDPE is particularly useful in adhesive compositions,including hot melt adhesives.

Thus, in a second aspect, the present invention provides a hot meltadhesive (HMA). The HMA comprises the MAH-g-LLDPE according to theinvention, a tackifier resin, and a wax.

In a third aspect, the present invention provides a process forpreparing the MAH-g-LLDPE. The process comprises:

(a) melting a LLDPE in an extruder to form a molten LLDPE;

(b) introducing maleic anhydride into the extruder; and

(c) contacting the molten LLDPE with the maleic anhydride in theextruder at conditions effective to increase the melt index (MI) of theLLDPE and to form the MAH-g-LLDPE. The MAH-g-LLDPE has a MI of 250 to800 g/10 minutes and comprises 0.01 to 3 weight percent of maleicanhydride, based on the weight of the MAH-g-LLDPE.

DETAILED DESCRIPTION OF THE INVENTION

A maleic anhydride grafted linear low-density polyethylene (MAH-g-LLDPE)with a unique combination of useful properties has been surprisinglydiscovered. These useful properties include a low density, a high meltindex, and greater adhesion over a wide temperature range. TheMAH-g-LLDPE, as an additive, can also enhance the properties of existinghot melt adhesive formulations.

Thus, in one aspect, the present invention provides a linear low-densitypolyethylene (LLDPE) grafted with maleic anhydride. The MAH-g-LLDPE hasa melt index (MI) of 250 to 800 g/10 minutes and comprises 0.01 to 3weight percent of maleic anhydride, based on the weight of theMAH-g-LLDPE.

Prior to grafting, the LLDPE generally has a density in the range of0.880 to 0.930 g/cm³. Preferably, the LLDPE has a density of 0.880 to0.928 g/cm³, 0.880 to 0.925 g/cm³, 0.880 to 0.923 g/cm³, 0.880 to 0.920g/cm³, 0.880 to 0.918 g/cm³, 0.890 to 0.930 g/cm³, 0.890 to 0.928 g/cm³,0.890 to 0.925 g/cm³, 0.890 to 0.923 g/cm³, 0.890 to 0.920 g/cm³, 0.890to 0.918 g/cm³, 0.900 to 0.930 g/cm³, 0.900 to 0.928 g/cm³, 0.900 to0.925 g/cm³, 0.900 to 0.923 g/cm³, 0.900 to 0.920 g/cm³, or 0.900 to0.918 g/cm³. After grafting, the density of the MAH-g-LLDPE may increaseslightly from the initial density of the LLDPE (e.g., +0.001 to 0.010g/cm³).

LLDPEs are generally copolymers of ethylene and one or more α-olefinshaving 3 to 10 carbon atoms. Examples of such olefins include propylene,1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methyl-1-pentene,1-decene, and the like. Preferred LLDPEs include copolymers of ethyleneand one or more α-olefins selected from 1-butene, 1-hexene, and1-octene. The copolymers generally have an ethylene content ranging from50 to 99.5 wt %, 70 to 99.5 wt %, or 80 to 99.5 wt %.

Before grafting, the LLDPEs useful in the present invention generallyhave a melt index in the range of 0.1 to 10 g/10 min., 0.5 to 10 g/10min., 0.5 to 5 g/10 min., or 0.5 to 1 g/10 min.

LLDPEs having these characteristics are available commercially frommanufacturers such as Westlake Chemical Corporation and Dow ChemicalCompany. Alternatively, they may be made according to methods known inthe art such as that described in U.S. Pat. No. 7,652,113 B2.

Preferably, the MAH-g-LLDPE has a maleic anhydride content of 0.1 to 2wt % or 0.5 to 1.5 wt %. The amount of MAH grafting is sometimesreferred to as the acid number, where 1 wt % of MAH grafting isequivalent to an acid number of approximately 5.67.

Preferably, the MAH-g-LLDPE according to the invention has an MI in therange of 300 to 800 g/10 min., 350 to 800 g/10 min., 400 to 800 g/10min., 450 to 800 g/10 min., 500 to 800 g/10 min., 300 to 750 g/10 min.,350 to 750 g/10 min., 400 to 750 g/10 min., 450 to 750 g/10 min., 500 to750 g/10 min., 300 to 700 g/10 min., 350 to 700 g/10 min., 400 to 700g/10 min., 450 to 700 g/10 min., 500 to 700 g/10 min., 300 to 600 g/10min., 325 to 600 g/10 min., 350 to 600 g/10 min., 375 to 600 g/10 min.,400 to 600 g/10 min., 300 to 550 g/10 min., 325 to 550 g/10 min., 350 to550 g/10 min., 375 to 550 g/10 min., 400 to 550 g/10 min., 425 to 550g/10 min., or 450 to 550 g/10 min.

The MAH-g-LLDPE according to the invention may be prepared by a processcomprising the steps of:

(a) melting a LLDPE in an extruder to form a molten LLDPE;

(b) introducing maleic anhydride into the extruder; and

(c) contacting the molten LLDPE with the maleic anhydride in theextruder at conditions effective to increase the melt index (MI) of theLLDPE and to form the MAH-g-LLDPE.

Any LLDPE described herein may be used in step (a), including a LLDPEhaving a density of 0.880 to 0.930 g/cm³, 0.880 to 0.925 g/cm³, 0.880 to0.920 g/cm³, 0.900 to 0.920 g/cm³, or 0.900 to 0.918 g/cm³.

The process according to the invention may be conducted in a continuousor batch mode, with continuous being preferred. The process may becarried out in any extruder typically used to process polyethylenes,such as single or multi-screw extruders. Multi-screw extruders aregenerally preferred, with a twin-screw extruder being most preferred. Ingeneral, the twin-screw extruder has two shafts that are preferablyintermeshing, and that may be either co-rotating or counter-rotating. Asused herein, the term “intermeshing” describes shafts that fit togethersuch that the shafts rotate in coordination with each other in closeproximity without mechanical interference. The term “co-rotating”describes shafts rotating in the same direction. And the term“counter-rotating” describes shafts rotating in opposite directions.

The extruder typically contains multiple barrels and zones havingvarying temperatures. Each zone may have one or more barrels. Some zonesare operated primarily to melt the polyethylene, while other subsequentzones are operated primarily to lower the viscosity (vis-break) of thepolyethylene and/or to facilitate grafting of the maleic anhydride ontothe polyethylene. These latter zones are sometimes referred to asreaction zones. The maleic anhydride (MAH) may be introduced either inliquid or solid form into any of the melting zones or reaction zones, orany combination of melting zones and reaction zones. Preferably, the MAHis introduced as a liquid into a barrel of the extruder where thepolyethylene is predominately, mostly, or entirely in molten form. Forthis purpose, the MAH may be melted before being fed into the extruder.

The LLDPE fed into the extruder may be in the form of pellets or reactorpowder/fluff/granules.

Typically, sufficient MAH is added to the extruder to yield the desiredgrafting level. For purposes of the present invention, the desiredgrafting level includes 0.01 to 3 weight percent, 0.1 to 2 weightpercent, and 0.5 to 1.5 weight percent of maleic anhydride, based on theweight of the grafted polymer.

To increase the MI of the LLDPE and to form the MAH-g-LLDPE of thepresent invention, the extruder is usually operated with a temperatureprofile ranging from 80 to 600° C. or more typically from 80 to 450° C.The extruder normally has a screw speed of 300 to 600 revolutions perminute (rpm). And the LLDPE typically has an average residence time inthe extruder of 1 to 5 minutes or more typically 2 to 4 minutes.

The MI of the product can be controlled by the screw speed, the feedrate of the LLDPE, and/or the degree of shear mixing imparted to thepolymer.

The grafting reaction in step (c) is preferably carried out in theabsence of an added free radical initiator, even though it is commonlyused in other grafting processes.

In a preferred embodiment, the process of the invention includes ventingvolatiles near the outlet of the extruder. It is preferred that theventing be conducted at a pressure less than atmospheric, such as undervacuum.

The grafted polymer product may be recovered by means known in the art,such as by passing the molten product to an underwater pelletizer or byextruding it through a die into strands, which are cooled in a waterbath and subsequently pelletized.

The MAH-g-LLDPE according to the invention has good adhesion to a numberof surfaces including nylon, polyvinyl alcohol, polystyrene,polycarbonate, polyolefins (e.g., polypropylene), epoxy resins, andmetals (e.g., aluminum and iron). It also has good adhesion to groundtire rubber, glass and other silicon dioxide substrates, and metal oxidesubstrates as a functional binder. In addition, the inventive materialhas excellent adhesion to typical substrates commonly used in thepackaging industry, such as paper, paperboard, cardboard, and kraftpaper. As such, the MAH-g-LLDPE is particularly useful as an adhesive byitself or may be blended with traditional additives to make adhesivecompositions, such as hot melt adhesive compositions. In addition tobeing particularly suited as a base polymer for a hot melt adhesive, theMAH-g-LLDPE according to the invention has a wide range of uses, such asa carpet backing, a compatibilizer in polymer mixtures, and as a tielayer in a multilayer structure. The multilayer structures may includeone or more layers of chipboard, aluminum foil, polyethylene, mylar,polypropylene, polyvinylidene chloride, ethylene-vinyl acetate, andkraft paper.

Moreover, the MAH-g-LLDPE can be used as an asphalt modifier to improveinterfacial adhesion in asphalt emulsions and asphalt blends as well ascan form inner penetrating networks with propylene polymers andcopolymers.

The MAH-g-LLDPE of the invention may be blended with one or moreconventional additives in typical amounts to prepare usefulcompositions. Examples of the additives include nucleating agents, heatstabilizers, antioxidants, lubricants, antistatic agents, dispersants,neutralizing agents, foaming agents, plasticizers, anti-foaming agents,flame retardants, crosslinking agents, viscosity enhancers, ultravioletlight absorbers, light stabilizers, slip agents, anti-blocking agents,dyes, pigments, natural oils, synthetic oils, waxes, fillers, andrubbers.

The MAH-g-LLDPE according to the invention is suitable for use in anumber of articles of manufacture, such as containers, films, laminates,and coatings. In one embodiment, the article of manufacture is apackage. The package may comprise two surfaces of a packaging material,such as cardboard or paperboard, bonded to each other by an adhesivecomposition according to the invention. The packaging article may be acarton, case, or tray.

As noted, the MAH-g-LLDPE according to the invention is particularlyuseful in hot melt adhesives (HMAs).

Thus, in another aspect, the invention provides a HMA comprising theMAH-g-LLDPE, a tackifier resin, and a wax.

HMAs typically contain a base polymer, a tackifier resin, and a wax. TheMAH-g-LLDPE according to the invention may be used as all or part of thebase polymer. Alternatively, the MAH-g-LLDPE may be used as an additivefor HMAs. Whether used as a part or all of the base polymer or as anadditive, the MAH-g-LLDPE can improve the cohesive strength and/or thebonding strength of the HMA over a wide temperature window.

The HMA according to the invention may contain from 0.5 to 90% by weightof the inventive MAH-g-LLDPE. As the base polymer or a component of thebase polymer, the MAH-g-LLDPE may be used in amounts ranging from 30 to90% by weight, or preferably from 30 to 60% by weight. As a performanceenhancer, the MAH-g-LLDPE may be used in amounts ranging from 0.5 to 30%by weight, or preferably from 5 to 15% by weight. All percentages arebased on the total weight of the HMA.

In addition to the MAH-g-LLDPE, the HMA may contain one or moreconventional base polymers. Examples of conventional base polymersinclude polyolefins, such as polyethylenes (e.g., LDPE, LLDPE, HDPE, andmetallocene-catalyzed polyethylenes (mPEs)), atactic polypropylene, andpolybutene; ethylene copolymers, such as ethylene-vinyl acetatecopolymers (EVA) and ethylene-unsaturated carboxylic acid or estercopolymers (e.g., ethylene n-butyl acrylate copolymers); polyamides;polyesters; natural or synthetic rubbers, including styrene blockcopolymers; polyvinyl acetate and vinyl acetate-unsaturated carboxylicacid or ester copolymers; and polyurethanes.

The HMA according to the invention may contain from 30 to 90% by weightof the base polymer, or preferably from 30 to 60% by weight. Allpercentages are based on the total weight of the HMA.

In one embodiment, the base polymer comprises a mPE. The mPE istypically a copolymer of ethylene and a C₄ to C₈ α-olefin comonomer, andmore typically a copolymer of ethylene and butene-1 or octene-1. The mPEtypically has an MI of at least 100 g/10 minutes, more typically of atleast 200 g/10 minutes, and most typically of 500 to 2000 g/10 minutes.The mPE may be present in the HMA in an amount ranging from 30% to 60%by weight, based on the weight of the HMA.

Examples of commercially available mPEs include Affinity® and Engage®polymers from Dow Chemical Company. Polymers and adhesives of this typeare described in U.S. Pat. Nos. 6,107,430 and 6,319,979.

The tackifier resins or tackifiers suitable for use in the HMAs of thepresent invention are not particularly limiting. Examples of tackifiersinclude (a) aliphatic and cycloaliphatic petroleum hydrocarbon resinsand the hydrogenated derivatives thereof; (b) aromatic petroleumhydrocarbon resins and the hydrogenated derivatives thereof; (c)aliphatic/aromatic petroleum derived hydrocarbon resins and thehydrogenated derivatives thereof; (d) aromatic modified cycloaliphaticresins and the hydrogenated derivatives thereof; (e) polyterpene resinsand hydrogenated polyterpene resins; and (f) copolymers and terpolymersof natural terpenes, styrene/terpene, α-methyl styrene/terpene, andvinyl toluene/terpene. Mixtures of two or more tackifiers may be used.

The Ring & Ball Softening Point, as determined by ASTM E-28, of thetackifier may be in the range of 70 to 140° C., 80 to 140° C., or 90 to140° C.

The HMA according to the invention may contain from 15 to 40% by weightof the tackifier, or preferably from 25 to 35% by weight. Allpercentages are based on the total weight of the HMA.

The wax suitable for use in the HMAs of the present invention are notparticularly limiting. Examples of useful waxes include (1) lowmolecular weight (100-6000 g/mol) polyethylenes; (2) petroleum waxes,such as paraffin wax having a softening point from 130 to 170° F. andmicrocrystalline wax having a softening point from 135 to 200° F.; (3)metallocene-catalyzed propylene-based waxes; (4) metallocene-catalyzedor single-site catalyzed waxes (e.g., those described in U.S. Pat. Nos.4,914,253; 6,319,979; WO 97/33921; and WO 98/03603); (5) synthetic waxesmade by polymerizing carbon monoxide and hydrogen, such asFischer-Tropsch wax; and (6) polyolefin waxes. Other materials that canbe used as the wax include hydrogenated animal, fish, and vegetable fatsand oils, such as hydrogenated tallow, lard, soy oil, palm oil,cottonseed oil, castor oil, etc. These hydrogenated materials are oftenreferred to as “animal or vegetable waxes.” Mixtures of two or morewaxes may be used.

The HMA according to the invention may contain from 5 to 30% by weightof the wax, or preferably from 10 to 20% by weight. All percentages arebased on the total weight of the HMA.

The HMA may also include one or more stabilizers or antioxidants. Thestabilizers are typically used to help protect the polymer componentsfrom thermal and/or oxidative degradation, which can occur during themanufacture or application of the HMA as well as during normal exposureto ambient conditions. A typical stabilizer includes pentaerythritoltetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate) (CAS#6683-19-8),which is commercially available as Irganox® 1010 or BNX® 1010.

The stabilizers may present in the HMA in typical amounts, such as from0.1 to 1% by weight, based on the total weight of the HMA.

The HMA may also include other traditional additives in typical amounts,such as nucleating agents, heat stabilizers, lubricants, antistaticagents, dispersants, neutralizing agents, foaming agents, plasticizers,anti-foaming agents, flame retardants, crosslinking agents, viscosityenhancers, ultraviolet light absorbers, light stabilizers, slip agents,anti-blocking agents, dyes, pigments, natural oils, synthetic oils,fillers, and rubbers.

The adhesive compositions of the invention, including the HMAs, may beprepared by techniques known in the art. For example, the ingredientsmay be placed in a jacketed vessel equipped with a stirrer and heated toan elevated temperature, for example, in the range of 120 to 200° C.Once the solid ingredients are melted, stirring may be initiated for asufficient time to form a homogeneous mixture, and then the mixtureallowed to cool. The precise temperature used would depend on themelting point of the particular ingredients and the viscosity of thefinished adhesive composition. The mixing may be performed under aninert gas atmosphere (such as nitrogen) or under a mild vacuum.

The adhesive compositions of the invention can be applied to substratesby techniques known in the art, such as extrusion, slot coating, spiralspray, melt-blown, spray-splatter, screen-printing, or roll-coating bydelivery from bulk reservoirs capable of controlling the temperaturewithin a range of, for example, 120 to 200° C.

The present invention includes and expressly contemplates any and allcombinations of embodiments, features, characteristics, parameters,and/or ranges disclosed herein. That is, the invention may be defined byany combination of embodiments, features, characteristics, parameters,and/or ranges mentioned herein.

As used herein, the indefinite articles “a” and “an” mean one or more,unless the context clearly suggests otherwise. Similarly, the singularform of nouns includes their plural form, and vice versa, unless thecontext clearly suggests otherwise.

While attempts have been made to be precise, the numerical values andranges described herein should be considered to be approximations (evenwhen not qualified by the term “about”). These values and ranges mayvary from their stated numbers depending upon the desired propertiessought to be obtained by the present invention as well as the variationsresulting from the standard deviation found in the measuring techniques.Moreover, the ranges described herein are intended and specificallycontemplated to include all sub-ranges and values within the statedranges. For example, a range of 50 to 100 is intended to describe andinclude all values within the range including sub-ranges such as 60 to90 and 70 to 80.

The content of all documents cited herein, including patents as well asnon-patent literature, is hereby incorporated by reference in theirentirety. To the extent that any incorporated subject matter contradictswith any disclosure herein, the disclosure herein shall take precedenceover the incorporated content.

This invention can be further illustrated by the following examples ofpreferred embodiments thereof, although it will be understood that theseexamples are included merely for purposes of illustration and are notintended to limit the scope of the invention.

EXAMPLES

Analytical Measurements

In the following examples, the test procedures listed below were used toevaluate the properties of the LLDPE and the MAH-g-LLDPE product.

Density was determined in accordance with ASTM D2839-93 except for thefollowing:

a) The conditioning procedure as described in paragraphs 7.2 and 7.3 wasomitted.

b) The strand was conditioned for 30 minutes at 23° C.

c) The density was determined in accordance with ASTM D1505 immediatelyfollowing paragraph 7.4.

d) The density was determined by averaging the density values of atleast three test specimens. The maximum difference allowed between thelowest density test specimen and the highest density test specimen was0.0005 g/cm³. If this difference was >0.0005 g/cm³, then the test wasrepeated starting with paragraph 7.1.

Melt Index (MI), I₂, was determined in accord with ASTM D1238, Condition190/2.16 and reported as “g/10 min.”

Viscosity was measured according to ASTM D3237.

Gardner Color was determined according to ASTM D1544.

Peel Adhesion Failure Test (PAFT) was performed using ASTM D4498.

Shear Adhesion Failure Test (SAFT) was performed using ASTM D4498.

The Corrugated Bonds Test involved making glue-ups (0.5-inch wide stripsof the hot melt adhesive) and heat sealing the samples at 350° F. usinga typical 45-lb corrugated board stock from Inland Container. Thesamples were aged at refrigerator (approx. 37° F.) and freezertemperatures (approx. 10° F.) for 24 hours and pulled by hand. Thevalues reported are the average percent fiber tear of the bonds.

Examples 1-7 Preparation of Maleic Anhydride Grafted Polyethylene

Pellets of a linear low density polyethylene (LLDPE) produced byWestlake Chemical Corporation, Houston, Tex., were fed with a volumetricpellet feeder into the inlet hopper of a 25-mm twin-screw extruderhaving 12 barrels (grouped into three zones) and a die. The extruder had12 kneading/mixing elements in each of the three zones. The LLDPE wascomposed ethylene and 1-hexene, and was characterized by having an MI of0.5 g/10 min and a density of 0.906 g/cm³. The LLDPE was fed into theextruder at barrel 1 and melted. The molten LLDPE was thereafter passedfrom one barrel to the next until it reached the die. Molten maleicanhydride (MAH) was pumped into the extruder at barrel 4. A secondliquid injection port fed an anti-oxidant into the molten mixture atbarrel 12. Vacuum venting was also conducted at barrel 12. The resultantLLDPE was recovered by extruding the molten product into a standard coldwater stranding bath. The average residence time of the LLDPE in theextruder was 2.5 to 3.2 minutes. The melt index of the product wascontrolled by the screw speed and the feed rate of the LLDPE. The cooledstrands were subsequently chopped into pellets. The resultant graftedLLDPE product (MAH-g-LLDPE) was analyzed.

The process conditions used and the properties of the MAH-g-LLDPE arereported in Table 1.

TABLE 1 Example Number 1 2 3 4 5 6 7 Temp. Temp. Temp. Temp. Temp. Temp.Temp. (° C.) (° C.) (° C.) (° C.) (° C.) (° C.) (° C.) Extruder BarrelNo. 1 80 80 80 80 80 80 80 2 250 250 255 255 255 255 255 3 240 230 240240 240 240 240 4 290 270 240 240 240 240 255 5 420 405 425 425 425 425425 6 420 410 425 425 425 425 425 7 420 410 425 425 425 425 425 8 420410 425 425 425 415 425 9 420 410 425 425 425 425 425 10  290 250 200200 200 200 200 11  200 200 200 200 200 200 200 12  200 200 200 200 200200 200 Die 205 205 200 200 200 200 200 Screw 480 450 480 480 480 480480 Speed (rpm) Vacuum 29 29 29 29 29 29 29 (inch Hg) Pellet 7 7 7 7.57.3 7.3 7 Feeder Rate (lb/hr) Output 6.93 7.06 6.95 7.59 7.4 7.3 7.9Rate (lb/hr) MAH Feed 0.4 4 0.3 0.3 0.3 0.3 0.3 Rate (mL/min) MAH 60 8055 60 70 70 75 Pump Discharge Pressure (psi) MAH-g- 259 120 422 327 277209 306 LLDPE Melt Index (g/10 min) MAH-g- 5.6 3 not not not not notLLDPE measured measured measured measured measured Acid Number

Examples 8-10 Preparation of Hot Melt Adhesives

Hot melt adhesive blends were prepared by placing the desired quantitiesof each material listed in Table 2 in a beaker. The beaker was placed ina heating mantle connected to a controller capable of maintaining thevessel and contents at 180° C. A Silverstein stirrer with a 3-bladepaddle stirrer was lowered into the beaker, and when the contents of thebeaker melted, the stirrer was started. The beaker was fitted with ametal lid with a nitrogen inlet, and the entire beaker was kept undernitrogen for the duration. The materials were mixed for 30 minutes aftermelting and allowed to cool.

Each composition was then tested for the properties listed in Table 2.

MAH-g-LLDPE in Table 2 is the material produced from Example 1.

W40-014 is a vis-broken, unmaleated LLDPE. It was produced from the sameLLDPE used as the starting material in Example 1. It was vis-brokenusing the procedures of Example 1, but without the MAH. The vis-brokenLLDPE had a density of 0.909 g/cm³ and an MI of 330 g/10 min.

AFFINITY GA 1950 is a polyolefin plastomer from Dow Chemical Company.The plastomer is reported as having a density of 0.874 g/cm³, aBrookfield Viscosity at 350° F. (177° C.) of 17,000 cP, an MI of 500g/10 min., and a DSC melting point of 70° C.

TABLE 2 Example 9 Example 10 Example 8 (Comparative) (Comparative)Amount Amount Amount (wt %) (wt %) (wt %) Ingredient MAH-g-LLDPE 40 0 0W40-014 0 40 0 Affinity GA 1950 0 0 40 Sasol H1 25 25 25 (wax) Escorez5637 34.5 34.5 34.5 (tackifier) Irganox 1010 0.5 0.5 0.5 (anti-oxidant)Initial Properties Viscosity at 150° C. 4430 4370 2185 (cP) Viscosity at177° C. 2215 2240 1060 (cP) Gardner Color 3 1 1 PAFT 67 65 62 (° C.)SAFT 111 113 94 (° C.) Corrugated Bonds 0 0 50 at −20° C. (% fiber tear)Corrugated Bonds 25 0 100 at 2° C. (% fiber tear) Properties After 100hrs at 177° C. Viscosity at 177° C. 2385 2250 1070 (cP) Gardner Color 1415 13 Skin/Char Edge ring 30% scum clear

As seen from Table 2, the hot melt adhesive based on AFFINITY GA 1950(Ex. 10) had better adhesion than the non-maleated, vis-broken LLDPE(Ex. 9) and the non-optimized MAH-g-PE of Example 1 (Ex. 8), accordingto the Corrugated Bonds Test at reduced temperatures. However, thehigh-temperature adhesion (PAFT and SAFT values) of the non-optimizedMAH-g-LLDPE (Ex. 8) was good relative to the comparative cases. And thenon-optimized MAH-g-LLDPE (Ex. 8) was intermediate in thermal stabilitytesting.

Examples 11-13

Another MAH-g-LLDPE was made following the procedures described inExamples 1-7, except that a different screw was used to impart morekinetic energy/shear into the polymer. The screw had (1) more mixingelements into the first zone of the extruder and a reverse element after5 mixing elements to slow the polymer flow through the zone, (2)additional kneading blocks in the second zone (in place of conveyingelements), and (3) both kneading blocks and a reverse element in thefinal zone. The MAH-g-LLDPE product had an MI of 500 g/10 min. and anacid number of 4.5. It is designated as DA-27 in Table 3.

In each example, DA-27 was blended with the additives listed in Table 3using the procedure outlined in Examples 8-10 to make an adhesivecomposition. The composition was then tested for the properties listedin Table 3.

Example 14 (Comparative)

Pellets of Dow's AFFINITY GA 1950 were blended with the additives listedin Table 3 using the procedure outlined in Examples 8-10 to make anadhesive composition. The composition was then tested for the propertieslisted in Table 3.

Example 15 (Comparative)

Pellets of an ethylene-vinyl acetate (EVA) copolymer from Arkema soldunder the name EVATANE 28-420 was blended with the additives listed inTable 3 using the procedure outlined in Examples 8-10 to make anadhesive composition.

The EVA copolymer is reported as having a density of 0.950 g/cm³, avinyl acetate content of 27-29 wt %, an MI of 370-470 g/10 min., and amelting point of 66° C. The composition was then tested for theproperties listed in Table 3.

TABLE 3 Example Number 14 15 11 12 13 (Comp.) (Comp.) Amount AmountAmount Amount Amount (wt %) (wt %) (wt %) (wt %) (wt %) Ingredient DA-2740 60 40 — — EVATANE 28-420 — — — — 40 Affinity GA 1950 — — — 40 —EASTOTAC H100W 39.5 29.5 39.5 39.5 39.5 (tackifier) Sasol H1 19.5 9.5 019.5 10 (wax) EPOLENE N21 — — 19.5 — — (wax) Parafin Wax — — — — 9.5Irganox 1010 1 1 1 1 1 (antioxidant) Properties Initial Viscosity 17075866 3170 1210 967 at 177° C. (cP) PAFT  81.0/0.4  89.9/7.4  82.2/18.965.1/3.6 47.9/1.0 (° C.) SAFT 123.3/0.8 125.1/1.7 124.8/0.8 92.2/2.775.1/1.3 (° C.) Fiber Tear at 0° F. 100 (4x) 100 (4x) 100 (4x) 100 (4x)100 (4x) (%) Fiber Tear at 20° F. 100 (4x) 100 (4x) 100 (4x) 100 (4x)100 (4x) (%) Fiber Tear at 40° F. 100 (4x) 100 (4x) 100 (4x) 100 (4x)100 (4x) (%) Fiber Tear at Room 100 (4x) 100 (4x) 100 (4x) 100 (4x) 100(3x), 50 Temp. (%) Fiber Tear at 135° F. 100 (4x) 100 (4x) 100 (4x) 100(4x)  75 (3x), 25 (%)

As seen from Table 3, the hot melt adhesives (HMAs) containing DA-27 asthe base polymer (Exs. 11-13) had greater PAFT and SAFT values than thecomparative blends (Exs. 14 and 15), indicating improved cohesivestrength and better bonding performance. The fiber tear results showthat the HMAs containing DA-27 performed as well as or better than thecomparative blends over a wide temperature window.

Examples 16-18

Examples 11, 14, and 15 were repeated, but with only 35 wt % of the basepolymers DA-27, Affinity GA 1950, and Evatane 28-420, respectively. Theresults are shown in Table 4 below.

TABLE 4 Example Number 17 18 16 (Comparative) (Comparative) AmountAmount Amount (wt %) (wt %) (wt %) Ingredient DA-27 35 — — EVATANE28-420 — — 35 Affinity GA 1950 — 35 — EASTOTAC H100W 44.5 44.5 44.5(tackifier) Sasol H1 19.5 20 10 (wax) Parafin Wax 0 0 10 Irganox 1010 10.5 0.5 (antioxidant) Properties Initial Viscosity 1337 900 780 at 177°C. (cP) PAFT 77.1/10.5 65 48/4 (° C.) SAFT 118.5/3.6  93 71/2 (° C.)Fiber Tear at 0° F. 0, 75, 75, 100 100 50 (%) Fiber Tear at 20° F. 0, 0,50, 50 100 100 (%) Fiber Tear at 40° F.  0 (4x) 100 100 (%) Fiber Tearat Room  25 (4x) 100 100 Temp. (%) Fiber Tear at 135° F. 100 (4x) 100 75(%)

As seen from Table 4, the PAFT and SAFT values of the HMA containingDA-27 (Ex. 16) were greater than those of the comparative blends.

Examples 19-25

HMAs were prepared using the ingredients and proportions listed in Table5 following the general procedures outlined in Examples 8-10. The HMAswere then tested for the properties listed in Table 5.

Dow's AFFINITY GA 1950 was used as the base polymer in all of the HMAs.

DA-27 (an MAH-g-LLDPE according to the invention) was used as anadditive at two concentrations, and compared with two commerciallyavailable maleated polyethylene waxes, Honeywell A-C® 575 and A-C® 573.

A-C® 575 is reported has having a density of 0.92 g/cm³, asaponification number of 30-40 mg KOH/g, a Gardner color of 3 max, and aBrookfield viscosity at 140° C. of >1000 cps.

A-C® 573 is reported has having a density of 0.92 g/cm³, asaponification number of 3-6 mg KOH/g, a Gardner color of 2 max, and aBrookfield viscosity at 140° C. of 600 cps max.

The performance testing involved an Institute of Packaging Professionals(IoPP) heat resistance test T-3006 and a bonding performance test at 3conditioning temperatures. The IoPP T-3006 test is a bond cleavage testwhere the adhesive was used to bond two pieces of stock corrugatedcardboard together. The test was set up according to the IoPP testingprotocol. The highest temperature at which the bonds passed wasrecorded.

TABLE 5 Example Number 19^(a) 20 21^(b) 22^(b) 23 24^(b) Amount AmountAmount Amount Amount Amount 25^(b) (wt %) (wt %) (wt %) (wt %) (wt %)(wt %) Amount (wt %) Ingredient Affinity GA 35 33.1 33.1 33.1 33.1 33.133.1 1950 Eastotac 39.7 37.3 37.3 37.3 34.1 34.1 34.1 H130R Sasol H1 2524.3 24.3 24.3 22.5 22.5 22.5 DA-27 — 5 — — 10 — — A-C 575 — — 5 — — 10— A-C 573 — — — 5 — — 10 BNX 1010 0.3 0.3 0.3 0.3 0.3 0.3 0.3 PhysicalProperties Viscosity at 1735 2150 1680 1560 3300 1860 1600 300° F. (cP)Viscosity at 775 1050 730 720 1445 810 790 350° F. (cP) Gardner 2 3 4 34 5 2 Color 100 g PAFT 148 151 149 147 144 143 140 (° F.) 500 g SAFT 190207 188 197 219 188 203 (° F.) Performance Properties IoPP Failure 60 7565 70 85 70 70 Temp. (° C.) Bonding NFT SFT NFT NFT FFT SFT SFTPerformance at −18° C. Corrugated Bonding SFT SFT SFT PFT FFT PFT PFTPerformance at 2° C. Corrugated Bonding FFT FFT FFT FFT FFT FFT FFTPerformance at 23° C. Corrugated ^(a)= Control. ^(b)= Comparative. FFT =Full Fiber Tearing bond (85-100% FT). PFT = Partial Fiber Tearing bond(50-84% FT). SFT = Slight Fiber Tearing bond (20-49% FT). NFT = No FiberTearing bond (0-19% FT).

As seen from Table 5, the physical properties of the mixtures revealthat there was an effect, surprisingly, of adding DA-27 to the HMAblends. The 100 g PAFT of the DA-27 blends (Exs. 20 and 23) was slightlyraised over the control (Ex. 19) and the other maleated PEs tested (Exs.21-22 and 24-25). In addition, the 500 g shear value of the DA-27 blends(Exs. 20 and 23) was elevated when compared to the control (Ex. 19) andthe other maleated PEs tested (Exs. 21-22 and 24-25). These resultsindicate that the cohesive strength of the HMAs containing DA-27 as anadditive was higher than the other products.

The bonding results show that adding 10 wt % of DA-27 markedly improvedthe bonding performance of the HMA throughout the temperature rangetested. At 5 wt % loading, the HMA containing DA-27 was not aseffective, but it still outperformed the adhesives containing the othermaleated PE materials.

The IoPP results show that the trend for higher cohesive strength wasfollowed up to the 10 wt % loading level. There was a marked improvementin the IoPP value at both the 5 wt % and the 10 wt % loading levelscompared to the other maleated PEs.

The greater heat resistance and the improved bonding strength at freezertemperatures are good indicators that DA-27 is a beneficial additive inmetallocene-catalyzed polyethylene-based HMAs.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. A process for preparing a linear low-density polyethylene(LLDPE) grafted with maleic anhydride (MAH-g-LLDPE), the processcomprising: (a) melting a LLDPE in an extruder to form a molten LLDPE;(b) introducing maleic anhydride into the extruder; and (c) contactingthe molten LLDPE with the maleic anhydride in the extruder at conditionseffective to increase the melt index (MI) of the LLDPE and to form theMAH-g-LLDPE, wherein step (c) is carried out in the absence of an addedfree radical initiator, wherein the MAH-g-LLDPE has a MI of 250 to 800g/10 minutes and comprises 0.01 to 3 weight percent of maleic anhydride,based on the weight of the MAH-g-LLDPE and wherein the MI is measured inaccordance with ASTM D1238, Condition 190/2.16.
 2. The process accordingto claim 1, wherein the extruder has a temperature profile ranging from80 to 600° C.
 3. The process according to claim 1, wherein the extruderhas a temperature profile ranging from 80 to 450° C.
 4. The processaccording to claim 1, wherein the polyethylene has an average residencetime in the extruder of 1 to 5 minutes.
 5. The process according toclaim 1, wherein the polyethylene has an average residence time in theextruder of 2 to 4 minutes.
 6. The process according to claim 1, whereinthe extruder has a screw speed of 300 to 600 revolutions per minute. 7.The process according to claim 1, wherein the MAH-g-LLDPE comprises 0.5to 1.5 weight percent of maleic anhydride.
 8. The process according toclaim 1, wherein the LLDPE has a density of 0.880 to 0.925 g/cm³beforegrafting.
 9. The process according to claim 1, wherein the LLDPE of theMAH-g-LLDPE is a copolymer of ethylene and 1-butene, 1-hexene, 1-octene,or mixtures thereof.
 10. The process according to claim 1, wherein theLLDPE has an MI of 0.5 to 10 g/10 minutes before grafting.
 11. Theprocess according to claim 1, wherein the MAH-g-LLDPE has an MI of 300to 800 g/10 minutes.